1. Field of the Invention
The present invention relates to a display device. Particularly, the present invention relates to a display device which makes it possible to switch to a mode in which an image to be seen is changed in accordance with a viewing direction.
2. Description of the Related Art
In recent years, electronic apparatuses have become lighter and lighter, so that an electronic apparatus, such as a portable phone or a mobile personal computer, which has a display can be taken out to and used in a public place. This has caused such a problem that a confidential document or information that a user wishes to individually browse is seen by a person near the user.
In response to this problem, there has been proposed a display device which can be set in a wide viewing angle display mode under normal conditions and which can be switched to a narrow viewing angle display mode when taken out to and used in a public place. The narrow viewing angle display mode refers to a mode in which a user right in front of a display can see a normal display image and in which a plain image or another image is seen from an oblique direction. Further, by making it possible to switch to the wide viewing angle display mode, it is possible to deal with a situation where a wide viewing angle is required, e.g., where a shot image needs to be seen by a large number of people.
Examples of a part for carrying out such a display include a viewing angle variable element disclosed in Japanese Unexamined Patent Application No. 105958/1997 (Tokukaihei 9-105958 (Patent Document 1); published on Apr. 22, 1997). According to the viewing angle variable element, a narrow viewing angle is obtained when liquid crystal molecules of a liquid-crystal layer provided between a pair of substrates are oriented in a direction perpendicular to the substrates, and a wide viewing angle is obtained when the liquid crystal molecules are oriented in a direction parallel to the substrates. Further, Japanese Unexamined Patent Application No. 62094/2004 (Tokukai 2004-62094 (Patent Document 2); published on Feb. 26, 2004) describes viewing angle changing means for changing a viewing angle of information means by changing the orientation of liquid crystals provided between two glass plates.
Furthermore, there is a display device arranged so as to be divided into several zones, for, example, in which liquid crystals are oriented in different directions. With this arrangement, in cases where a display is seen from a direction other than the front direction in a narrow viewing angle display mode, an image different from an image shown by the display can be seen. For example, Japanese Unexamined Patent Application No. 264768/2001 (Tokukai 2001-264768 (Patent Document 3); published on Sep. 26, 2001) discloses a liquid crystal display device in which orienting films sandwiching liquid crystals therebetween are divided into a plurality of regions and in which the regions adjacent to one another have different directions of orientation. Further, Japanese Unexamined Patent Application No. 38035/2004 (Tokukai 2004-38035 (Patent Document 4); published on Feb. 5, 2004) discloses a liquid crystal display device in which first and second liquid crystal cells having different viewing directions are alternately provided.
However, a recent portable phone has a display section which is vertically positioned so as to be normally observed and which is horizontally positioned so as to display a television image or the like. This caters to the increasing number of scenes where the user chooses by himself/herself where the display section faces.
On the other hand, in either of Patent Documents 1 and 4, viewing angle control carried out in a narrow viewing angle display mode can only prevent an image from being seen obliquely from one direction (horizontal direction). That is, the image can be prevented from being seen obliquely from right and left directions, but cannot be prevented from being seen obliquely from upper and lower directions.
Thus, according to the conventional techniques, the viewing angle control can only prevent an image from being seen from right and left directions. Therefore, in cases where the display section is observed in its normal vertical position, the user's privacy is protected by controlling a viewing angle. However, in cases where the display section is observed in its horizontal position, the viewing angle control prevents the image from being seen from upper and lower directions, so that the user's privacy cannot be protected from anyone who is on either side of the user.
Further, see a case where a user standing in a train uses a mail function of a mobile phone. In this case, even when the display section is used in its vertical position, a person standing behind the user may be able to glance over the user's shoulder at the display. In order to prevent an image from being seen from a backward direction in such a case, it is important to prevent the image from being seen obliquely from upper and lower directions. For this reason, the narrow viewing angle display mode is required to prevent an image from being seen obliquely from upper and lower directions as well as right and left directions.